Explain why we must balance all chemical equations.

Answer is: The chemical equation must be balanced so that it follows the law of conservation of mass.

For example, ablanced chemical reaction:  

Pb(NO₃)₂(aq) + Li₂SO₄(aq) → PbSO₄(s) + 2LiNO₃(aq).

According to law (principle) of mass conservation, number of atoms must be equal on both side of balanced chemical reaction.  

There are two lithium atoms, one lead atom, one sulfur atom, ten oxygen atoms and two nitrogen atoms on both side of reaction.

A chemical equation should be balanced because of law of mass conservation.

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